This paper examines the relationship between global energy security and climate change policy. There are growing concerns about the sustainability of the future supply of hydrocarbons. The energy system is the single largest source of anthropogenic greenhouse gases, therefore it is no surprise that decarbonising the supply of energy services is a key element of climate change policy. The central proposition of this paper is that the world faces a global energy dilemma: can we have secure, reliable and affordable supplies of energy and, at the same time, manage the transition to a low-carbon energy system? The paper is divided into five sections. The first section considers the contemporary challenges to global energy security, focusing on the possibility that in the future oil production might not be able to meet demand. The second section considers how the perils of climate change are forcing us to rethink the very meaning of energy security such that a low-carbon energy revolution is now called for. The third section explains that while the developed world is largely responsible for the anthropogenic carbon emissions currently in the atmosphere, a global shift in energy demand is underway and over the next 20 years it is the developing world that will contribute an ever-increasing share of global emissions. The fourth section introduces the notion of the global energy dilemma nexus to explain how the processes of globalisation are the driving force behind this global shift in energy demand and carbon emissions. The final section explains how the global energy dilemma nexus plays itself out in different ways across the globe. The conclusions suggest that human geography can make a significant contribution to social science research on energy security and climate change.